Lymphocyte DNA from 14 donors positive for HTLV-I/HTLV-II antibodies and from four donors with unknown serology were tested for the presence of HTLV-I and HTLV-II proviral DNA by PCR. Ten sets of primer pairs representing the GAG, POL, ENV, TAX and LTR gene sequences of HTLV-I or HTLV-II were used for amplification. Two new sets of primer pairs, one specific for HTLV-I GAG, GP1/GP2, and the other for HTLV-II LTR, LT1/LT2, were designed by this laboratory. All reactive samples had a detectable HTLV-I or HTLV-II POL sequences. Among the seropositive donors, 6/14 were positive for HTLV-l POL, 11/14 positive for HTLV-II POL and 6/14 were dually reactive for HTLV-I/HTLV-II POL. PCR amplification and hybridization with oligoprobes detected multiple genes in 6/14 serpositive donors, suggesting the presence of complete genome in these DNA samples. Positive amplification with primers for 2 or more gene sequences was detected in 11/18 DNA samples. 3/14 seropositive donors failed to amplify HTLV-I or HTLV-II sequences with any of the primer pairs tested. 2/4 untested random donors of unknown serology were positive for HTLV-I or HTLV-II sequences. Southern blot hybridization with a full length HTLV-I or HTLV-II probe showed the presence of complete HTLV-I genome in lymphocyte DNA of 1 donor and HTLV-II genome in 4 DNA samples. Among the samples positive by PCR and Southern blot hybridization, two were specific for HTLV-I, eight were specific for HTLV-II and one was dually reactive for HTLV-I/HTLV-ll.